In recent years, as proposed in Appl. Phys. Lett., Vol. 67, Issue 21, pp. 3114-3116 (1995) by Stephan Y. Chou et al., a technology for transferring a fine pattern provided on a mold onto a semiconductor, glass, resin, metal or the like has been developed and has received attention. This technology is called nanoimprint or nanoembossing since it has resolving power on the order of several nanometers. By utilizing this technology, it is possible to process a three-dimensional structure at a wafer level at the same time. For this reason, the technology has been expected to be applied to production technologies of optical devices such as photonic crystal, and production technologies of structures such as μ-TAS (Micro Total Analysis System) and biochips.
In a processing technology using such a nanoimprint, when it is used in a semiconductor fabrication technology etc., for example, a fine pattern on a mold is transferred onto a substrate or a member on the substrate in the following manner.
First, on the substrate (e.g., a semiconductor wafer), a layer of photocurable resin material is formed.
Then, the mold on which a desired pattern is formed is pressed against the resin layer, followed by irradiation with ultraviolet rays to cure the resin material. As a result, the pattern formed on the mold is transferred onto the resin layer.
Thereafter, etching is effected by using the resin layer as a mask, whereby the pattern of the mold is formed on the substrate.
During the transfer of the pattern formed on the mold in the imprint technology, in order to effect a high-resolution fine processing by improving transfer precision, it is necessary to measure a distance (gap) between the mold and the substrate.
U.S. Pat. No. 6,696,220 B2 has described a method of measuring the gap between the mold and the substrate by an interferometer. U.S. Pat. No. 6,696,220 B2 has also disclosed a gap measurement method capable of measuring the gap by appropriately designing a shape of the mold even when the gap (distance) is a distance of ¼ or less of a wavelength of light used for a measurement with the interferometer. The gap measurement method will be described with reference to FIG. 8.
In the case where a distance 706 between a first surface 702 of a mold 701 and a surface 704 of a substrate is ¼ or less of a measurement wavelength, it is difficult to accurately measure the distance 706 by an interferometer. In the gap measurement method described in U.S. Pat. No. 6,696,220 B2, a measuring area is provided at a position different from a position at which the first surface 702 is formed. In the measuring area, a second surface 703 is additionally provided. By such a constitution, when a distance between the second surface 703 and the substrate surface 704 is ¼ or more of the measurement wavelength, it is possible to measure the distance between the second surface 703 and the substrate surface 704. For this reason, by measuring a distance 705 between the first surface 702 and the second surface 703 in advance, a value of the distance 706 is capable of being measured even when the distance is ¼ or less of the measurement wavelength.
Incidentally, in these days of increased need for high-resolution fine processing, a further improvement in imprint accuracy of the above-described nanoimprint is required.
However, the gap measurement method disclosed in U.S. Pat. No. 6,696,220 B2 is not necessarily satisfactory for such a need.
More specifically, the distance 705 between the first surface 702 and the second surface 703 cannot be measured since these surfaces are not opposite to each other. Accordingly, the distance 705 and a distance between the second surface 703 and the substrate surface 704 are required to be measured by a method other than that using the interferometer. However, when these two distances are measured by the method other than that using the interferometer, there arises such a problem that a measurement error is liable to occur.
Further, U.S. Pat. No. 6,696,220 B2 has also described the need for an optical system different in constitution from an optical system for effecting measurement of the distance between the mold and the substrate in order to measure in-plane positions of the mold and the substrate. In the method described in U.S. Pat. No. 6,696,220 B2, in-plane alignment is effected based on data obtained by the in-plane position measurement. Incidentally, the term “in-plane” is used with respect to a plane parallel to a processing surface of the mold, and the in-plane positions are represented by X, Y, and θ. Further, the distance (gap) between the mold and the substrate is represented by Z.
An apparatus using nanoimprint is such a processing apparatus that a size ratio between the mold and an imprint pattern is 1:1, unlike an apparatus for reduction exposure such as a stepper or the like. For this reason, at a rearward position from a back surface of the mold, a spatial constraint condition is stringent compared with the case of the stepper or the like. For example, a pattern area at the processing surface of the mold is 26×36 mm and an objective lens used in the optical system has a diameter of approximately 20 mm, so that these dimensions are of the same order.
Accordingly, as described in U.S. Pat. No. 6,696,220 B2, when the optical system for effecting the distance measurement and the optical system for effecting the in-plane position measurement are separately provided, it is difficult to dispose these optical systems together in the same area. For this reason, there is a problem such that it is difficult to prevent an error in distance measurement caused by positional deviation between the mold and the substrate due to a temperature change, vibration, etc.